The present invention relates generally to the field of antennas and in particular to a new and useful method and apparatus for producing small physical size plasma device antennas having large antenna apertures resulting from matching the plasma device operating frequency to that of a transmitted or received signal.
Traditionally, antennas have been defined as metallic devices for radiating or receiving radio waves. Therefore, the paradigm for antenna design has traditionally been focused on antenna geometry, physical dimensions, material selection, electrical coupling configurations, multi-array design, and/or electromagnetic waveform characteristics such as transmission wavelength, transmission efficiency, transmission waveform reflection, etc. As such, technology has advanced to provide many unique antenna designs for applications ranging from general broadcast of RF signals to weapon systems of a highly complex nature.
Included among these antennas are omnidirectional antennas, which radiate electro-magnetic frequencies uncontrolled in multiple directions at once, such as for use broadcasting communications signals. Usually, in the absence of any additional antennas or signal attenuators, an omnidirectional radiation lobe resembles a donut centered about the antenna. Antenna arrays are known for producing a directed transmission lobe to provide more secure transmissions than omnidirectional antennas can. Known antenna arrays require many powered antennas all sized appropriately to interfere on particular frequencies with the main transmitting antenna radiation lobe, and thereby permit transmission only in the preferred direction. Antenna arrays normally have a significant footprint, which increases greatly as the angular width of the transmission lobe is reduced.
Generally, an antenna is a conducting wire which is sized to emit radiation at one or more selected frequencies. To maximize effective radiation of such energy, the antenna is adjusted in length to correspond to a resonating multiplier of the wavelength of frequency to be transmitted. Accordingly, typical antenna configurations will be represented by quarter, half, and full wavelengths of the desired frequency.
Plasma antennas are a newer type of antenna which produce the same general effect as a metal conducting wire. Plasma antennas generally comprise a chamber in which a gas is ionized to form plasma. The plasma radiates at a frequency dictated by characteristics of the chamber and excitation energy, among other elements. Plasma antennas are generally known for use in a wide range of applications. See, for example, U.S. Pat. Nos. 6,657,594, 6,369,763, 6,046,705, and 5,963,169.
In particular, U.S. Pat. No. 6,657,594 discloses an antenna system in which a plasma antenna is operated at a frequency near the resonant frequency of plasma to form a more efficient radiator requiring a smaller size than metallic antenna. Plasma resonance frequency can refer to a variety of wave types which become resonant, such as plasma ion acoustic waves, plasma electrostatic waves, and plasma electromagnetic waves. However, matching of plasma frequency, as it is defined in the present invention, to operating frequency is not disclosed.
U.S. Pat. No. 6,492,951 teaches a plasma antenna as well, but also does not disclose matching of plasma frequency to operating frequency.
The inventor herein has also developed plasma loop antennas, as described in U.S. Pat. No. 6,700,544, arrays of plasma element among other variable conductive elements to form antennas in U.S. patent application Ser. No. 10/648,878 filed Aug. 27, 2003, now U.S. Pat. No. 6,870,517, and reconfigurable scanners using the plasma elements in U.S. patent application Ser. No. 10/693,477 filed Oct. 24, 2003, now U.S. Pat. No. 6,922,173, the entirety of each of which is incorporated herein by reference as if set forth in full. Any of the antennas described therein can be configured and used in the invention described further herein.
As is known in the field, efficient transfer of RF energy is achieved when the maximum amount of signal strength sent to the antenna is expended into the propagated wave, and not wasted in antenna reflection. This efficient transfer occurs when the antenna is an appreciable fraction of transmitted frequency wavelength. That is, the antenna geometry is matched to the incident or transmitted frequencies expected to be encountered. The antenna will then resonate with RF radiation at some multiple of the length of the antenna. Due to this, metal antennas are somewhat limited in breadth as to the frequency bands that they may radiate or receive because their length is not easily or accurately adjusted. Often, antennas used to transceive signals across a range of signals will have an antenna geometry selected to most closely match that of a center frequency in the intended operating frequency range. This results in an increasingly inefficient antenna as the frequencies of the incident signals progress toward the ends of the range.
Recently, wireless communications have become more and more important, as wireless telephones and wireless computer communication are desired by more people for new devices. Current wireless communications are limited to particular ranges of the electro-magnetic frequency spectrum. High-speed communications are limited by the selected frequency spectrum and number of users which must be accommodated. For example, 3G networks can presently provide a maximum data transfer rate of up to 2 Mbps, shared among network users.
Growth in the demand for wireless communications makes clear that more and more such devices will be needed for a variety of functions. And, different devices of the same type may still operate on different frequencies within a selected range to avoid interference. As consumers become used to high-speed Internet connections at home and work, they will demand efficient wireless data transfer as well. Therefore, there is a need to provide a more efficient, yet portable, antenna for quickly adapting to provide maximum aperture and efficiency at any number of frequencies.
Further, from a manufacturing standpoint, it is more efficient to install one type and size antenna into each of several types of devices or different versions of the same device, and subsequently configure the antenna in a particular device to operate on a selected frequency, independent of the geometry. Such capability would provide greater flexibility in the miniaturization of portable devices, as the geometry of the antenna would no longer be limiting by the design; alternatively, the design of the device would not be limiting by the transceiving efficiency.